This invention relates to a pumping apparatus having a wear end and a pump end having an internal pumping means to prevent liquid in the pump end from entering the wear end. More particularly, this invention relates to a sealless pumping apparatus having a pump end and a wear end wherein a rotor portion of the wear end is sealed from a stator portion of the wear end and wherein an internal pumping means is provided to prevent liquid in the pump end from entering the wear end.
Pumps generally include a pump end where incoming liquid is pressurized for subsequent recovery through an outlet and a wear end where the parts subject to wear such as bearings, shaft, thrust washers, driven magnet or the like are located. Pumps of all types, including centrifugal, gear or screw pumps rely on a seal or a magnetic drive or a canned motor design in order to minimize leakage from the pump. The relatively simple designs of the sealed pumps have a seal which will wear and, therefore, eventually leak.
In canned motor design pumps and magnetic drive pumps, the rotating portion inside the pump is separated and sealed from the stator portion of the pump or the drive magnet portion respectively by means of a seal known as a can, lining or shell. The can prevents fluid in the rotor portion from contacting the stator portion of the wear end. Since a rotating shaft does not rotate through the can, there is no need to provide a seal between the can and rotor portion of the pump. The can portion of the pump is formed of a metallic or plastic composition to render it resistant to a variety of liquids being pumped, particularly hydrocarbon compositions. However, the type of liquids that can be pumped also is limited such as acidic compositions which degrade the can metallic composition, slurries, the solid portion of which rapidly deteriorate the wear end and hot liquid composition which also deteriorate the wear end. In the case of slurries, it has been proposed to utilize a screen or a filter between the pump end and the wear end to eliminate contact between the solid portion of the slurry and the wear end. The use of filter screens is undesirable since they become rapidly plugged thereby depleting the wear end of needed heat exchange and lubricating liquid. In addition, in magnetic drive pumps, the use of metallic cans creates eddy current losses which produce undesirable heat that must be removed from the wear end. In addition, since presently available canned motor pumps and magnetic drive pumps rely upon the liquid being pumped to effect lubrication and heat removal in the wear end, they cannot be run dry accidently without destroying the pump. With either of the magnetic drive or canned motor sealless pump designs, the units do not have seals but they do have internal bearings and thrust washers and shafts which depend on the fluid being pumped for lubrication. Accordingly, these parts will wear over time as well. In the event that the liquid being pumped is non-lubricating, abrasive or crystalline or very hot or cold, the bearings, washers and shafts can be damaged quickly and render the pumps either too expensive or impractical to repair.
When utilizing a liquid in the wear end for lubrication, antifriction bearings such as roller bearings or ball bearings cannot be used. Generally, sleeve bearings are used which are of higher cost and have less predictable life than antifriction bearings.
U.S. Pat. No. 4,290,611 discloses a pumping seal utilizing a plate having spiral grooves as a pump. U.S. Pat. No. 5,090,712 discloses a pumping seal having an alternative discontinuous grooved surface.
Accordingly, it would be desirable to provide a pump which prevents liquid being pumped from entering a wear end of a pump. This will allow the use of the pump in slurries, low viscosity or thin liquids, high temperatures, afford "run dry" protection and greatly extend the life of the wear end. It would also be desirable to provide a magnetic drive pump which can utilize a nonmetallic can in order to avoid eddy current loss.
In addition, it would be desirable to avoid liquid in the wear end to permit use of antifriction bearings and to provide more sensitive detection of unwanted liquid in the wear end but removes the negative aspects of the nonmetallic can being the only seal to the environment.